Numerous patents use inclined lateral grooves to improve traction. The patent U.S. Pat. No. 4,298,046 by Herbelleau et al includes slits that are inclined with respect to a normal to the tread and closely spaced between lateral grooves to give improved adherence upon braking or acceleration. Slits inclined in a direction of rotation (forward) were located in the two lateral zones of the tire width while those in the center zone were inclined in an opposite direction. Under load the tire starts to become worn to cause directed wear of the tire contact surface, typical of heel-toe wear. The forward inclined slits were designed to be active in longitudinal acceleration (driving) and slits in the opposite direction were designed to be active in braking.
The French patent FR 1548673 by Devienne shows saw-tooth tread block elements having oblique faces or teeth on one of the bands (ribs) being crossed with regard to the oblique faces or teeth of the adjacent band (rib). The two bands are separated by a groove parallel to the equatorial plane. The purpose of the invention being to improve driving as well as braking adhesion by alternating oblique faces across the tread width. The same tire would be used on all axles of the vehicle.
The German patent DE 8707957 by Frisch has scales, or short tread blocks, arranged circumferentially in rows. Circumferential grooves between rows of tread block form circumferential ribs. A sharp leading edge on the tread block improves the driving traction of each tread block. Alternating ribs or rows having leading and trailing sharp edges respectively, provide both forward and reverse driving assistance. The same tire is used on all axles of the vehicle.
A variable incline on the faces of tread blocks is disclosed in the U.S. Pat. No. 4,186,788 patent by Pommier. The tractor tires of this patent have tread lugs where the leading edge of the lugs have an angle between the lug contact surface and its leading face in the center of the tread width smaller than the same angle at each shoulder segment. This unidirectional tire does not have ribs as such and these angles are obtuse. This patent discloses that abnormal (uneven) wear disappears giving way to uniform wear which lengthens the life of the tire. The primary purpose of this patent is to control adherence without regard to tangential stresses as wear progresses. The non-directional tire of this invention has well defined ribs and is also used as a non-drive axle tire.
The U.S. patent application Ser. No. 07/590303 by Remick is a unidirectional drive axle tire with tread blocks having smaller inclined lateral groove angles with respect to the radial direction at their leading face than at their trailing face. This vehicle tire, designed primarily for heavy trucks, has significant improvements in uneven wear and the life of the tire. The groove angles result in the leading edge, or corner, of each tread block being more abrupt, but angles greater than 90 degrees are maintained. A defined variation in these angles from the lateral edges to the center of the tire width is not specified. The attempt to control longitudinal tangential stress at the contact surface is not disclosed in this application, and using the tire on a non-drive axle while reversing its rotation is not discussed.
This background information does not teach one skilled in the art how to design the tire tread using reverse cut or sloping lateral grooves to reduce wear, nor is it obvious to extend the scope of any patent or combine patents to obtain the tread design of the invention. No prior art is known to the inventors that suggests reversing the rotation of the tire when used on non-drive axle compared with the drive axle to reduce overall wear of the vehicle's tires. Only patent U.S. Pat. No. 4,298,046 suggests groove angles having large angles between a normal to the contact surface and the center axis of the groove such that acute angles exist at the edge of the tire contact surface and the groove. However, the purpose of this patent was to produce wear that increased tire traction. The invention reduces uneven wear and extends the tire's life.